Problem: $1\dfrac{2}{7} \div \left(-2\dfrac{1}{4}\right) = $
Explanation: Let's start by converting the mixed numbers to fractions. $\phantom{=}1\dfrac{2}{7} \div \left(-2\dfrac{1}{4}\right)$ $=\dfrac{9}{7}\div\left(-\dfrac{9}{4}\right)$ $=\dfrac{9}{7}\cdot\left(-\dfrac{4}{9}\right) ~~~~~~~\text{multiply by the reciprocal}$ $=\dfrac{{1}\cancel{9}}{7}\cdot \left(- \dfrac{4}{{1}\cancel{9}}\right)$ $=\dfrac{1}{7}\cdot\left(-\dfrac{4}{1}\right)$ $=-\dfrac{4}{7}$